1. Field of the Invention
The present invention relates to a lens barrel adapted for use in a photographic camera, a video camera or the like.
2. Related Background Art
In the lens barrel of a conventional phototaking (interchangeable) lens adapted to be mounted on a camera body, a motor for driving a focusing lens, gears, a main circuit board with electrical parts etc. are mounted on a fixed tube member used for mounting on the camera body. In such lens barrel, the focusing operation is conducted by controlling the motor by an electrical focusing signal, supplied for example from a focus state detecting device in the camera body, and linearly moving the focusing lens along the optical axis by the driving force of the motor.
In such lens barrel, the motor, gears and main circuit board are mounted, in the fixed tube member, in the vicinity of the mount portion used for coupling with the camera body. For this reason, in the axial movement of the focusing lens for focusing operation, the diaphragm unit and the motor for driving the diaphragm unit are also axially moved. Consequently said motor and the main circuit board have to be connected through a flexible circuit board, and each component inevitably becomes complex.
Also in the conventional photographic camera or video camera, a motor and gears for driving the focusing lens are incorporated in a part of the fixed tube member of the lens barrel, as proposed for example in the Japanese Utility Model Laid-Open Application No. 62-140512. In the automatic focusing mode, the motor is driven by a driving (focusing) signal from a focus state detecting device in the camera body, and the driving (rotating) force of the motor is transmitted to a rotary helicoid member, which is rendered rotatable with respect to the fixed tube member, constituting a part of the lens barrel, thereby linearly moving, in the axial direction, a lens support member, which supports a phototaking (focusing) lens, and is in helicoid coupling with the rotary helicoid member.
Also in the manual focusing mode, the focus state detecting device is deactivated, and the focusing operation is conducted by disconnecting a part of the members for transmitting the driving force of the motor and manually rotating a focusing member.
In the conventional driving mechanism for the lens support member, employing a helicoid member, the helicoid member has to be incorporated with satisfactory precision during assembly and the presence of such helicoid member tends to complicate the entire structure, to increase the number of assembling steps and to render the adjustment of assembly more difficult.
Furthermore, if the rotary and linearly moving helicoid member are to be formed with a plastic material, the helicoid screw has generally to be molded with a mold structure divided into three parts, which tend to be complicated in structure and expensive in cost.
Also FIG. 5 shows, in a cross-sectional view, a lens barrel proposed in the Japanese Utility Model Laid-Open Application No. 62-140512. Referring to FIG. 5, a fixed tube member 41 is provided, at an end thereof, with a bayonet mount 41A for coupling with a camera body (now shown). A first movable ring 42 and a second movable ring 44 respectively support focusing lenses L4-L6 and L1-L3. The second movable ring 44 is provided, on the external periphery thereof, with a fitting portion 44a for fitting with an internal periphery portion 42a of the first movable ring 42, and fixing means for fixing the second movable ring 44 to the first movable ring 42. The fixing means is composed of plural projections 44b, 44b, . . . protruding from the external periphery of the second movable ring 44 and engaging with engaging portions 42b, 42b, . . . , provided on the internal periphery of the first movable ring 42.
A motor 46 supported on the fixed tube member 41 consists of a stator, composed of yokes 46a1, 46a2 fixed on the fixed tube member, a permanent magnet (not shown) etc. and a rotor composed of coils, a rotary shaft 46b etc. Gears Gl-Gn linked with the rotary shaft 46b and constituting a gear train for varying the revolution, are supported by a plate member 48 fixed on the fixed tube member 41.
A rotary ring 50, rendered rotatable in a fixed position of the fixed tube member 41, is provided, on the internal periphery thereof, with a helicoid portion 50a engaging with a hellicoid portion 42c formed on the external periphery of the first movable ring 42, and, on the external periphery, with a V-sectioned ball lace groove 50b for supporting bearing balls 52.
The bearing balls 52 are positioned along the groove 50b of the rotary ring 50 in continuous or spaced manner by a ball spacer 54, and are supported by a first ball receiving ring 56, which is fitted in the internal periphery of the fixed tube member 41 and is provided, at an end, with a sloped face, and by a second ball receiving ring 58 screwed on an internal screw 41a of the fixed tube member 41.
A plate-shaped spacer 60 is provided between the first ball receiving ring 56 and the fixed tube member 41, for regulating the pressure on the balls 52, by the thickness of the spacer. A position detector 62, such as an encoder, is provided in the gear mechanism.
The rotary ring 50 is formed with a smaller diameter in a part of its external periphery, and a gear ring 64 is fixed on the smaller diameter portion 50c and meshes with an output gear of the gears Gl-Gn.
In the above-explained structure, a space for accommodating the motor 46 and the gears Gl-Gn is formed between the movable ring 42 and the fixed tube member 41, and is maintained by members 50, 56, 58 constituting the bearing for the balls 52, 52, . . . and fixed between the fixed tube member 41 and the movable ring 42.
A diaphragm unit D is fixed by the internal periphery and a smaller diameter wall 42e of the movable ring 42, and a motor EMD for driving the diaphragm unit D is fixed thereon.
A rigid printed circuit board 70 bears electrical circuits for driving the motors 46 and EMD. The board 70 is connected with the motor 46 through a flexible printed circuit board (not shown). The board 70 is positioned in a gap between the first movable ring 42 and the mount 41A, and is fixed to the fixed tube member 41.
A contact block 71, for electric signal exchange with the camera body (not shown), is connected, by soldering 71a, with the rigid printed circuit board 70.
A rear cover 69 is fitted in the internal periphery of the bayonet mount 41A. A flexible printed circuit board 72 extends, from a connecting portion 72a with the motor EMD, through a hole 42d in the first movable ring 42, then is bent toward the lens mounting aperture of the camera body, further bent toward the camera body in the space inside the fixed tube member 41 and is soldered at an end 72c to the rigid printed circuit board 70.
In the structure shown in FIG. 5, the motor 46 is driven according to a lens driving signal transmitted from the camera body. The rotating torque of the motor 46 is transmitted, through the gears Gl-Gn, to the rotary ring 50, thereby rotating the ring 50 in the fixed position. The rotation of the rotary ring 50 axially moves the first movable ring 42 through the helicoid portion 42c, while the first movable ring 42 is prevented from rotation by key means (not shown). Thus the second movable ring 44 moves together with the first movable ring 42, whereby the lenses L1-L6 are moved axially.
In such mechanism, the flexible printed circuit board 72 follows the movement of the first movable ring 42, and the position of the bent portion 72b of the board 72, between the fixed tube member 41 and the first movable ring 42, moves according to the movement of the first movable ring 42.
In the above-explained conventional lens barrel, the flexible printed circuit board 72 is designed to follow the relative movement of the fixed tube member 41 and the first movable ring 42, by a portion parallel to the optical axis and positioned along the fixed tube member 41 and the first movable ring 42, and a bent portion 72b positioned between the fixed tube member 41 and the first movable ring 42.
Consequently the flexible printed circuit board may be broken by twisting if the first movable ring 42 rotates about the optical axis, and can only follow the axial movement thereof.
In order to enable the flexible printed circuit board to also follow the rotation of the first movable ring 42, there has to be constructed a part that can follow the rotation by extracting such rotating movement, and the structure becomes inevitably complex.
Also the conventional lens barrel of the phototaking (interchangeable) lens, to be mounted on a camera body, includes a fixed tube member (external lens tube) and a focusing member rotatable about the optical axis. These members are formed by resin molding for weight reduction, and are mutually coupled in such a manner that the focusing member is rotatably supported for example by a shouldered member and is prevented, for example by a screw, from disengagement from the fixed tube member.
Such fixed tube member and focusing member, formed by resin molding, do not have sufficient mechanical strength and are apt to be deformed by external pressure, thus resulting in troubles that, for example, the focusing member cannot be properly rotated.
Also the rotation of the focusing member cannot be smooth because the resin-molded sliding portion thereof is in contact with the similarly resin-molded sliding portion of the fixed tube member.
Furthermore, the conventional lens barrel of the phototaking (interchangeable) lens to be mounted on a camera body includes, as principal components, a fixed tube member (external lens tube) and a mount member to be mounted on the camera body. In front of the fixed tube member there is provided a rotatable focusing member (focusing ring), and, inside the fixed tube member there are provided a lens support member axially movable following the movement of the focusing member, a diaphragm unit, a motor for driving said diaphragm unit etc.
In general, the fixed tube member and the mount member are constructed as separate components, in consideration of the assembling process and the adjustment at the assembly.
Because of such separate structure, the assembling of the conventional lens barrel is generally conducted by fitting the focusing the focusing member from the front side (object side) of the fixed tube member, then assembling the motor and gears for rotating the focusing member, from the rear side (camera body side) of the fixed tube member, and finally fitting the mount member at the rear end of the fixed tube member.
As the conventional lens barrel includes the above-mentioned fixed tube member, and mount member which are relatively large external components, the structure of the lens barrel becomes inevitably complex with an increased number of component parts and with complex steps of assembly and adjustments.
Furthermore, the conventional lens barrel of the phototaking (interchangeable) lens to be mounted on a camera body includes a lens support member, for holding the lens, and a cylindrical support member of a different external diameter, for holding the lens support member. Such lens support member and cylindrical support member of different external diameters are mutually fixed by a screw or an adhesive material, as proposed in the Japanese Patent laid-Open Application No. 58-78132.
Such fixing operation of the lens support member and the cylindrical support member in the conventional lens barrel, employing a screw or an adhesive material, requires a significant amount of time for assembly, adjustment and disassembling, thus leading to a high production cost.
Furthermore, the focusing of a phototaking lens is achieved by a manual focusing in which a focusing member (focusing ring) is manually rotated, or by an automatic focusing in which the focusing member is driven by a motor according to a focusing signal obtained by a focus state detecting device of the camera body.
Such automatic focusing is achieved by rotating the focusing member by transmitting the rotating force of a motor through a gear mechanism provided on the fixed tube member of the lens barrel, and the switching of the focusing operation is in most cases done by a selector switch provided on the fixed tube member.
Also in many lens barrels, the lens support member, supporting the focusing lens, is driven by a motor through gear means including plural gears, and such gear means generally incorporates a friction structure, in order to prevent destruction of the gears by an external impact force.
Such conventional friction structure includes input and output gears mutually coupled by friction, for example by a spring, on a common shaft, and the driving torque is transmitted from the input gear to the output gear by the frictional force. When an abrupt external force is applied to the gear means, the two gears mutually rotate against the biasing force of the spring, thereby preventing the destruction of the gears.
However, such friction structure is associated with a complicated structure with a large number of components, such as two divided gears, spring member, stoppers such as E-rings and washers, involving a large number of assembling steps.